string operations - weird characters - c

Question

Description:
I read userinput (e.g "ls -l /") with fgets() and invoke Parse() where it gets seperated ("ls" "-l" "\") for later usage.
The Problem is: the tokens from the the first cycle have weird characters(screenshot below) in it, but from thereon the output is fine.
I tried to initialize both Buffers with zeroes with no change in behaviour. Please explain what is happening in my first output.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/times.h>
#include <sys/wait.h>
#include <signal.h>
#include <errno.h>
typedef char* string;
char inputBuffer[512];
string parse[256];
int j,parseCount;
void Parse(void);
void Parse(void)
{
char buffer[512];
string token;
token = " ";
strcpy(buffer, inputBuffer);
j=0;
parse[j] = strtok (buffer, token);
while (parse[j] != NULL)
{
j++;
parse[j] = strtok (NULL, token);
}
parseCount =j;
}
int main (void)
{
printf(">> ");
fgets(inputBuffer, 512, stdin); /* input buffer, max.Input(char), whereFrom?*/
Parse();
for (j=0;j<parseCount;j++){
printf("[%d] %s\n",j, parse[j]);
}
return main();
}

Answer 1

This line
parse[j] = strtok (buffer, token);
stores memory addresses in buffer, which is local to Parse(). The memory representing buffer is invalidated upon the return of Parse(), so also the addresses stored in parse aren't valid anymore when trying to be dereferenced to print what they refer to.
To fix this have the calling function create a temporary working buffer and pass down to `Parse() a reference to it:
char * parse[256] = 0;
char buffer[512] = "";
size_t parseCount = 0;
void Parse(char * buffer)
{
const char * token = " ";
size_t j = 0;
parse[j] = strtok(buffer, token);
while (parse[j] != NULL)
{
j++;
parse[j] = strtok(NULL, token);
}
parseCount = j;
}
int main(void)
{
fgets(buffer, 512, stdin);
{
char buffer_tmp[512];
strcpy(buffer_tmp, buffer);
Parse(buffer_tmp);
for (size_t j = 0; j < parseCount; j++)
{
printf("[%zu] %s\n", j, parse[j]);
}
}
return 0;
}
As I don't like the globals, I'd prefer the following:
#include <stdio.h>
#include <string.h>
size_t parse(char * buffer, char ** parse)
{
const char * token = " ";
size_t j = 0;
parse[j] = strtok(buffer, token);
while (parse[j] != NULL)
{
j++;
parse[j] = strtok(NULL, token);
}
return j;
}
#define IN_MAX (512 + 1 + 1)
int main(void)
{
char buffer[IN_MAX] = "";
if (NULL != fgets(buffer, IN_MAX, stdin))
{
char buffer_tmp[IN_MAX];
strcpy(buffer_tmp, buffer);
{
size_t parse_count = 0;
char * parse[IN_MAX/2 + 1] = 0;
size_t parse_count = parse(buffer_tmp, parse);
for (size_t j = 0; j < parse_count; j++)
{
printf("[%zu] %s\n", j, parse[j]);
}
}
}
else if (ferror())
{
fprintf(stderr, "Error reading from inout stream.\n");
}
return 0;
}